A track roller assembly and a reduction gear apparatus of a construction machine are equipped with ferrous floating seal parts for the purpose of preventing leakage of lubrication oil from inside thereof as well as entering of earth and sand therein. Accordingly, such floating seal parts are widely produced by applying adequate treatment in which a seal sliding surface thereof is quenched to have a hard martensite structure, or a large amount of hard cementite and Cr7C3 carbide of 30% by volume are crystallized in the seal sliding surface while causing a parent phase to a martensite by quenching, in order to improve seizing resistance and abrasion resistance. Such an exemplary floating seal part is made by using a Ni-hard cast iron (having a typical composition of carbon of 2.7 to 3.5 wt %, Si of 0.4 to 1.0 wt %, Mn of 0.4 to 0.6 wt %, Ni of 4.2 to 4.7 wt % and Cr of 1.4 to 2.5 wt %), a high-carbon and high-Cr cast iron (for example, carbon of 3.3 to 3.6 wt %, Cr of 15 to 17 wt %, Mo of 2.5 to 3.5 wt % and V of 0.2 to 0.5 wt %) (for example, as shown in Japanese Patent Publication (KOKAI) No. S51-59007).
In addition, a ferrous floating seal part in which cladding abrasion-resistant material containing of WC and self-fluxing alloy is splayed to a seal sliding surface thereof is sometime used for some purposes.
In the ferrous floating seal part used for sealing a lubricating oil in the reduction gears and the track rollers, a seal sliding surface thereof is abraded as fine particles of earth and sand are entered on the seal sliding surface by hulling motion in the earth and sand, and is lubed with the sealed lubrication oil therein. Accordingly, a ferrous floating seal part capable of withstanding a very severe lubrication condition is required. Even in a case of a most conventionally used hard ferrous floating seal part made of a high-carbon and high-Cr cast iron, when setting pressure (press force) at assembling is high, considerable quenching crack (heat crack), seizing and abnormal abrasion occur on the seal sliding surface, resulting in leakage of oil.
And, even if various tool steels such as a cold work tool steel and a high speed steel (SKH material) are applied so as to increase the seizing resistance and the abrasion resistance, seizing due to defect of seizing resistance easily occurs, resulting in insufficient heat crack resistance and abrasion resistance. In addition, since such steels are so expensive that a material costs would increase in view of material yields before a product is finished.
Further more, in resent years, construction machines such as bulldozer are required to be driven at a high speed for improvement in working efficiency, and therefore, the ferrous floating seal part necessarily rotates at a high speed. This also causes quenching crack, seizing and abnormal abrasion, resulting in leakage of oil.
In order to solve the above-mentioned problem, an object of the present invention is to provide ferrous seal sliding parts excellent in heat crack resistance, seizing resistance and abrasion resistance and a producing method thereof.